Fuse construction



May 27, 1941- s. l. LINDELL 2,243,107

FUSE CONSTRUCTION Filed Aug. 3, 1940 4 Sheets-Sheet 1 By wu/Mmwm ggg/6 May 27, 1941` s. LINDELL 2,243,107

FUSE CONSTRUCTION 7n vere for.' l'gumzfzmdelz May 27, 1941. s. L INDELL y FUSE CONSTRUCTION Filed Aug. 3, 1940 4 Sheets-Sheet 4 .www

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Jnveno Jgwrzf uw@ Patented May 27', 1941 2,243,101 FUSE coNs'mUc'noN sima I. Linden, chicago, n1., signor t lSchweitxer Conrad, Inc., Chicago, Ill., a corporation of Delaware Application August 3, 1940, Serial No. 350,776

(Cl. 20o-135) 18 Claims.

This invention relates, generally, to circuit interrupting apparatus, and it has particular relation to the construction of fusible elements for circuit interrupters of the fuse type.

An object of this invention is to provide for definitely and permanently controlling the current division between a low melting point core and a high melting point sheath of a composite fusible element.

A further object of this invention is to provide a fusible element which will maintain substantiallyrconstant its time-current characteristics throughout its life. 4

Another object of this invention is to provide for taking advantage of the properties .of silver and ytin in a fusible element in a new and improved manner. I

Another object of this invention is to prevent alloying between a tin core and a lsilver sheath of a fusible element.

f It is another object of this invention to provide for rapidly conducting heat away from the tin core of a fusible element having a silver sheath and for preventing the conduction o hat to the tincore.

Another object of this invention is to deform relatively infusible terminals onto the ends of A nature and scope of this invention reference may be had to the following detailed description taken in `connection with the accompanying drawings, in which:

Figure` 1 is a. view, partly in side elevation and partly in section, showing the silver sheath of a .composite fusible element;

Figure 1 is aV view in side elevation showing the construction of the core that is intended to be iitted into the sheath shown in Figure 1;

Figure 3 is a sectional view of the composite fusible element having terminals at its ends;

Figure 4 shows how a terminal can be deformed onto one. end of the composite fusible element;

Figure 5 is a longitudinal sectional view of'a replaceable fuse link, certain parts being shown in elevation, in which is embodied the composite fusible element of the present invention;

Figure 6 is a longitudinal sectional view, certain parts being shown in elevation, of a replaceable cartridge in which the fusible element of the present invention is embodied;

Figure 7 is a view, at an enlarged scale, showing how the fusible element for the cartridge shown in Figure 6 is constructed;

Figure 8 is a View illustrating the method of deforming the terminals onto the ends of the fusible element shown in Figure 7;

Figure 9 is a longitudinal sectional view ofv a portion of a solid material type of fuse in which the composite fusible element of the present invention is embodied;

Figure 10 is a View, at an enlarged scale, showing the details of construction of the fusible element for the fuse shown in Figure 9;

Figure 11 is a longitudinal sectional view of a liquid type of fuse in which the composite fusible element of the present invention is embodied;

Figure 12 is a detail sectional view taken along the line |2I2 of Figure 11; and

Figure 13 is a detail sectional view taken along the line I3-i3 of Figure 12.

The present invention constitutes an improvement over the construction shown in the copending application of Triplett, Serial No. 144,789, led May 26, 1937.

Referring now particularly to Figures 1,Y 2 and 3 of the drawings, it will be observed that the reference .character III designates, generally,` a composite fusible element which has a sheath I I that isformed of relatively high melting point high conductivity metal such as silver. 'I'he sheath Il is shown by itself in Figure 1, and,

as there indicated, it may be formed of silver that is dead soft annealed. The sheath il may be formed of other material having similar characteristics such as copper. .Howeven silver il preferred.

Within the sheath Il there is a core that la formed principally of low melting point metal such as tin. The core in its entirety is indicated at I2 in Figure 2 and comprises an intermediate tin core portion I3 to the ends of which imperforate metal plugs I 4 are secured at butt joints l5. The plugs I4 are formed of metal which is capable of conducting heat rapidly away from the tin core i3 and which is capable of plugs Il are preferably` formed of hard drawn silver.

The plugs I4 are secured to the ends of the tin core by heat and fusion. If the plugs I4 are formed of hard drawn silver they can be heated to about 300 C. and then they are placed at 'the ends of the tin core I3, the abutting faces having been previously cleaned by ux or grinding. Suicient heat is transferred from the plugs I4 to the ends of the tin core I3 so as to cause the desired fusion at the joints I5. The silver tin alloy joints I5 have approximately the same resistivity as the tin core I3 itself. Therefore, it is unnecessary to consider the resistance of these joints since it is substantially the same, as the resistance of the tin core I3 itself and therefore the resistance of the tin core is determined substantially only by its physical dimensions. This is important when the division of current flow between the sheathV II and the core I3 is considered.

It is important that there be no alloying action between the tin core I3 and the silver sheath II prior to actual operation of the composite fusible element to interrupt a circuit. It is for this reason that the core I2 is assembled separately from the sheath II. After the core I2 has been assembled and has cooled to room temperature, it is inserted into the sheath II. The internal diameter of the sheath II is just large enough to accommodate the core I2 readily and without a loose t. The silver plugs I4 at the ends of the tin core I3 within the silver sheath II seal the ends of the latter after terminals I6 are deformed thereon and prevent oxidation of the surface of the tin core I3.

The composite fusible element I is arranged to inter-connect relatively infusible massive terminals I6. It will be understood that the ter-l minals I6 arey merely illustrative of various types of terminals that can be employed in connection with the composite fusible element I0 as will hereinafter appear. Each of the terminals I6 is provided with a longitudinally extending aperture I1 which is of such diameter that the ends of the composite fusible element I0 readily flt therein. 'Ihe outer ends of the apertures I1 are beveled as indicated at I8 so that sharpcorners are not presented tothe adjacent surface of the sheath I I. It will be observed that the apertures I1 are of such depth that the butt joints I between the tin core I3 and the silver plugs I4 are well within the solid metal of the terminals I6 as indicated at I9. With this arrangement. when the l`composite fusible element I 0 is flexed or the terminals I6 are moved relatively to each other, there is 'no stress concentration along the joints I5 since they are fully protected by the terminals I6 themselves. The flexing that takes place will principally be concentrated along the lines 'where the composite fusible element I0 emerges from. the terminals I6 where the section of the core it and sheath Ill isr homogeneous. With the arrangement above described this line is through the solid tin of the core i3.

The ends of the composite fusible element Iare preferably secured to the terminals I6 by deform-= ing the latter onto the former. 'As indicated in Figure 4 of the drawings, the terminal I6 may be inserted in a suitably shaped opening 2li in a die 2i and then a punch 22 is moved downwardly into the opening 2li so as to deform the terminal I6 onto the end of the composite fusible element i0 within the same. This deforming operation provides intimate contact engagement between the terminal I G and the sheath il. Also the sheath II is deformed into intimate contact engagement with the plug I4 and a small portion of the tin core I3.

It Will vbe understood that the relative sizes of the silver sheath I I and the core I2 will vary depending upon the time-current characteristics that are desired. Thus, the sheath II and core I2 may be longer than that shown in the drawings or shorter and may have greater or lesser diameters as may be desired.

When the terminals I6 are deformed onto the ends of the composite fusible element II), there will be intimate contact between the silver plugs I4 and the silver sheath II. The joints at I5 between the silver plugs I4 and the tin core I3 have a definite resistance which is that of the tin core I3 itself. Thus the tin core I3 and the silver sheath I I are connected in parallel through joints of low resistance at which nooxidation can take place. Therefore, it is possible to accurately predetermine the time-current characteristics of the composite fusible element I0 since it is possible to determine accurately the division of current flow between they tin core I3 and the silver sheath I I. This is important even though the silver sheath II constitutes the principal current carrying element.

For purposes of illustration, the composite fusible element represented by the reference character I0 will be employed in the various embodiments of the invention disclosed. It will be y understood, however, that the actual proportions for the different embodiments will be different but for illustrative purposes they can be considered as being the same.

In Figure 5 of the drawings there is shown a renewable or replaceable fuse link construction that is similar to thefuse link construction shown in 'Iriplett application Serial No. 144,789, referred rto hereinbefore. In this embodiment of the invention the composite fusible element I0 has terminals 26 and 21 deformed onto its ends as previously described for Ithe terminals I6. The terminals 26 and 21 are also interconnected by a strain wire 28 which is formed of relatively high strength metal such as a nickel-chromium alloy. The strain wire 28 is inserted in the apertures of the terminals 26 and 21 along with the composite fusible element I0 and these terminals are deformed conjointly onto the ends of both the composite fusible element I0 and the strain wire 28v as will y be readily understood. The terminal 26 is provided with a flanged head 29 for connection to one line terminal while the terminal 21 is provided with a flexible lead 3I for connection to another line terminal. l

In Figure 6 of the drawings there is shown a cartridge for a solid arc extinguishing type of fuse such as that disclosed in the copending application of Triplett, Serial No. 223,175, filed August 5, 1938. The fuse cartnidge comprises relatively infusible terminals 34 and 35 that are arranged to be interconnected by a composite fusible element I0 and a strain wire 31 of the character previously described. The terminal 34 is rod-like in character and is arranged to move longitudinally through a bore 38 in sections 38 of solid arc extinguishing material such as borlc acid or magnesium berate. The sections 39 of solid arc extinguishing material are enclosed in a sleeve 48 of suitable insulating material. The rod-like terminal 34 is arranged to be connected to one line terminal. A flexible lead 4I is secured to the terminal 35 to permit connection to another lne terminal.

In Figure "i of the drawings, the arrangement of the composite fusible element in the terminals 34 and 39 is more clearly illustrated. In this embodiment of the invention a composite fusible element I is coiled intermediate its ends so that for a given distance between the terminals 94 and 35 a considerably greater length of fusible section therebetween is provided. This is desirable in order to obtain certain time-current characteristics. The ends of the composite fusible element I0 and the strain wire 31 are inserted in suitable apertures in the terminals I4 and 35, which are then deformed to secure the desired contact engagement. It willl be observed that the terminals 34 and 99 have beveled openings as indicated at 42 and 4I to prevent the applicacation of sharp edges to the silver sheath Il as previously described.

In Figure 8 of the drawings, the method of deforming the terminal 36 onto the ends of the composite fusible element III and the strain wire 31 is illustrated. The terminal 99 is placed in a suitable opening' in a die 44 with the composite fusible element Il and strain wire l1 in place. A punch 45 is then brought down upon the die 44 under suiiicien-t pressure to deform the terminal 95 and cause the metal thereof to flow around the ends of the composite fusible element i0 and the strain wire 31. l In Figure 9 of the drawings there is shown a fuse construction that is also shown in Triplett Patent No. 2,183,728, except for the fusible element I0. As illustrated, the composite fusible element Ill is provided for interconnecting terminals 48 and 49. The terminal 49 is in the form of a metallic fitting which is secured to a metallic sleeve, 50 that in turn is clamped to a ferrule I which forms one line terminal of the device. The ferrule Il is secured onto one end of a tubular insulating housing 52. The terminal 49 is rod-like in character and is arranged to be connected by flexible conductors 59 to a ferrule, not shown, at the other end of the housing 52. 'I'he rod-like terminal 49 is arranged to move through a longitudinal bore 54 in sections 55 of solid arc extinguishing material, such as boric acid or magnesium borate, under the influence of a coil tension spring 56. The rod-lilfe terminal 49 has a pin 51 projecting transversely through its lower end to which a strain element assembly, shown generally at 58, is connected for preventing movement of this terminal.l As illustrated, the strain element assembly 98 is connected to a pin 59 which projects inwardly from the metallic sleeve 50. When the composite fuse element I0 blows on flow of predetermined overcurrent, the entire current ilow is transferred to the strain element assembly 58 which parts and permits the rod-like terminal 49 to be withdrawn through the bore 54 as is fully described in Trlplett patent referred to hereinbefore.

The arrangement of the composite fuse element4 I0 in the terminals 49 and 49 is illustrated more clearly in Figure of the drawings. One end of the composite fusible element I0 is inserted in a suitable aperture in the terminal 48 so that the butt joint I5 is fully protected as previously described. The aperture is beveled as indicated at 60 to prevent the presentation of a sharp edge to the silver sheath I I. The terminal 49 isdeformed onto Ithe end of the composite fusible element I0 substantially as shown in Fig- I ure 4 of the drawings.

-It will be noted that the composite fusible element il is coiled several times intermediate its ends so as 'to provide a relatively great length of fusible element with a relatively short distance between the terminals 48 and 49.

It will be observed that the aperture in the terminal 49 is beveled as indicated at 6l for .the purpose set forth hereinbefore. Not only is the terminal 49 generally deformed onto the end of the composite fusible element but also it is locally deformed as indicated at B2 by use of a prick punch.

In Figure 1l of the drawings, there is shown va liquid fuse construction which, except for the composite fusible element I0, is substantially the same as shown in Conrad Patent No. 2,091,430. As illustrated, the composite fusible element i0 and a strain wire 61 are arranged to interconnect relatively infusible terminals 66 and 66. The terminal 66 is carried by a metallic spider 6l which is supported on a metallic ferrule B9 forming one line terminal of the device. The ferrule 99 is secured by suitable means onto one end oi' an insulating housing 10. The terminal 94 is arranged to be connected by flexible conductors 1i -to a ferrule, not shown, in the lower end of the housing 10. The terminal 66 is arranged to be retracted by a coil tension spring 1 1 when the composite fuse element I0 and the strain wire 61 have blown.

Surrounding the composite fuse element i0 and the strain wire 61 is a tubular arcing chamber 19 that is formed of suitable insulating material. The arcing chamber 181s carried by a ring 14 of insulation which, as shown, is threaded into the ferrule 69. The terminal 66 carries arms 1l, Figure 12, which support a liquid director 19 which, on retraction of the terminal B6 by the spring 12 is arranged to force liquid, contained in the housing 10 to the level shown, up into the arcing chamber 19 for extinguishing the are that is drawn between the terminals 65 and 96, all of which is described in detail in the Conrad patent referred to hereinbefore.

A composite fuse element I0 is inserted into suitable apertures in the terminals 65 and 66 which are deformed thereon as previously described. 'I'he construction for both is illustrated in Figure 13 in connection with terminal 66. As there shown, the aperture in the terminal 66 for receiving one end of the composite fusible element l0 is of sufllcient depth so that the butt joint Ii between Ithe tin core I3 and the silver plug I4 is fully protected. The aperture is beveled as indicated at 11 to prevent the application of a sharp edge to the silver sheath ii. Not only is the terminal 66v generally deformed onto the end of the composite fusible element il but also it is locally deformed as indicated at 18 by a prick punch.

Since certain further changes can be made in the foregoing constructions and different embodiments of the invention can be made without departing from the scope thereof, it is intended that all matter shown inthe accompanying drawings and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is: I

l. In a fuse, in combination, a core formed of metal having a relatively low melting point,A a sheath formed of metal having a relatively high melting point surrounding said core and extending beyond the ends of the same, and a plug formed of metal having a relatively high felting point lling each end of said sheath and inmetal having a relatively low melting point, a sheat formed of metal having a relatively high melting point surrounding said core and extend` ing beyond the ends of the same, a plug formed of metal having a relatively high melting point filling each end of said sheath and intimately bonded to the ends of said core'for conducting heat away therefrom, and a-relatively infusible terminal intertting with and deformed 'onto each end of said sheath.

3. In a fuse, in combination, a core formed of metal having a relatively low melting point, a sheath formed of metal having a relatively high melting point surrounding said core and extendlng beyond the ends of the same, an imperforate plug formed of metal having a relatively high melting point filling each end of said sheath and engaging the ends of said core for conducting heat away therefrom, and a relatively infusible terminal intertting with and deformed onto each end of said sheath, the deformed portions of said Iterminals overlapping theends of said core through a substantial extent whereby flexing of said sheath in the vicinity of the joints between said core and plugs is prevented.

4. In a fuse, in combination, a core formed of metal having a relatively low melting point, a sheath formed of metal having a relatively high melting point surrounding said core and extending beyond the ends of the same, a plug formed of metal having a relatively high melting point filling each end of said sheath and intimately bonded to the ends of said core for conducting heat away therefrom, and a relatively infusible terminal interfltting with and deformed onto each end of said sheath, the deformed portions of said terminals overlapping the ends of said core through a substantial extent whereby flexingiof said sheath in the vicinity of the joint between said core and plugs is prevented.

5. In a fuse, in combination, a tin core, a silver sheath' surrounding said core and extending beyond the ends of the same, and a plug formed of metal having a relatively high melting point filling each end of said sheath and intimately bonded to the ends of said core for conducting heat away therefrom.

6. In a fuse, in combination,` a tin core, a

silver sheath surrounding said core and extend. j

ing beyond the ends of the same, and a silver plug filling each end of said sheath and intimately bonded to the ends of said core for conducting heat away therefrom.

7. In a fuse,.in combination, a tin core, a silver sheathfsurrounding said core and extending beyond the ends of the same, a plug formed of metal having a relatively high melting point filling each end of said sheath and intimately bonded to the ends of said core for conducting heat away therefrom, and a relatively infusible terminal intertting with and deformed onto each end -of said sheath.

8. In a fuse, in combination, a tin core, a silver sheath surrounding said core and extending beyond the ends of the same, a silver plug filling each end of said sheath and engaging the ends of said core for conducting heat away therefrom, and a relatively infusible terminal intertting with anddeformed onto each end of said sheath, the deformed portions of said terminals overlapping the ends of said core through a substantial extent whereby flexing of said sheath in the "vicinity of the joints between ksaid core and plugs is prevented.

9. In a fu'se, in combination, a tin core, a silver sheath surrounding said core and extending beyond the ends of the same, a silver plug filling each end of said sheath and intimately bonded to the ends of said core for conducting heat away therefrom, and a relatively infusible terminal interiitting with and deformed onto each end of said sheath, the deformed portions of said terminals overlapping the ends of said core through a substantial extent whereby flexing of said sheath in the vicinity of the joints between said core and plugs is prevented.

10. In a fuse, in combination. a core formed of metal having a relatively low melting point. a sheath formed of metal having a relatively high melting point surrounding said core and extending beyond the ends of the same, and an imperforate plug formed of metal having a relatively high melting point filling each end of said sheath and engaging the ends of said core for conducting heat away therefrom. the composite element formed by said core and sheath being coiled intermediate its ends to provide a section the length of which is substantially greater than the distance between its end portions.

11. In a fuse, in combination, a tin core, an annealed silver sheath surrounding said core and extending beyond the ends of the same, and an lmperforate plug formed of metal having a relatively high melting point filling each end of said sheath and engaging the ends of said core for conducting heat away therefrom, the composite element formed by said core and sheath being coiled intermediate-its ends to provide a section the length of which is substantially greater than the distance between its end portions.

12. In a fuse, in combination, a tin core, an annealed silver sheath surrounding said core and extending beyond the ends of the same, a silver plug filling each end of said sheath and intimately bonded to the ends of said core for conducting heat away therefrom, and a relatively infusible terminal intertting with and deformed onto each end of said sheath. the deformed portions of said terminals overlapping the ends of said core through a substantial extent whereby flexing of said sheath in the vicinity of the Joints between said core and plugs is prevented, the composite element formed by said core and sheath being coiled intermediate its ends to provide a section the length of which is substantially greater than the distance between its end portions. 1

13. Method of making a core for a composite fusible element which comprises: securing by heat and fusion relatively high melting point metal plugs to the ends of a relatively low melting point metal core.

14. Method of making a composite fusible e1e, ment which comprises: securing by heat and fusion relatively high melting point metal plugs to the ends of a r'latively low melting point metal core and inser ing the plugs and core into a relatively high melting point metal` sheath.

15. Method of making a fuse link which comprises: securing by heat and fusion relatively high melting point metal plugs to the ends of a relatively low melting point metal core, inserting the plugs and core into a relatively high melting point metal sheath thereby forming a composite fusible element, and deforming relatively massive metallic terminal onto the ends of the composite fusible element.

16. Method of making a fuse link which comprises: securing by heat and fusion relatively high melting point metal plugs to the ends of a relatively low melting point metal core, inserting the plugs and core into a relatively high melting point metal sheath thereby forming a composite fusible element, and deforming relatively massive metallic terminals onto the ends of the composite fusible element in such manner that the areas of deformation overlap the ends of the core a substantial extent.

17. Method of making a fuse link which comprises: securing by heat and fusion relatively high melting point metal plugs to the ends of a relatively low melting point metal core, inserting the plugs and core into an annealed relatively high melting point metal sheath thereby forming a composite fusible element, and colllng the composite fusible element intermediate its ends to provide a section the length of which is substantially greater than the distance between its end portions.

18. Method of making a fuse link which comprises: securing by heat and fusion relatively high melting point metal plugs to the ends of a relatively low melting point metal core, inserting the plugs and core into an annealed relatively high melting point metal sheath thereby forming a composite fusible element, coiling the composite fusible element intermediate its ends to provide a section the length of which is substantially greater than the distance between its end portions, and deforming relatively massive metallic terminals onto the ends of the composite fusible element.

SIGURD I. LINDELL. 

